The invention relates to a method for controlling the operation of a rear light set of a vehicle tractor. The invention also relates to a vehicle comprising a tractor and a trailer or a semi-trailer, each having a rear light set. The present invention is also applicable to a train comprising a tractor, a trailer or semi-trailer and one or more additional trailers.
The invention can be applied in heavy-duty vehicles, such as trucks and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles.
The function of the rear lights of a vehicle is to indicate to a person outside the vehicle—such as the driver of another vehicle or a pedestrian—where the vehicle is located, and what its next movements will be. The rear lights are activated or deactivated following the driver's action, depending on the conditions (night or day, weather, etc.) and on how the driver intends to move the vehicle (forward motion, turning movement, braking action, etc.).
In a vehicle comprising a tractor and a trailer pivotably connected to the tractor, the trailer is generally equipped with a rear light set which is identical to the rear light set arranged on the tractor. Thus, a person outside the vehicle can be informed by the rear lights actuation both when the vehicle only consists of the tractor and when a trailer is connected to the tractor.
However, when a trailer is connected to the tractor, most of the time, the rear lights of the tractor's rear light set are not visible, as they are hidden by the trailer. Then, only the rear lights of the trailer rear light set can provide the required information to a person outside the vehicle. Nevertheless, in such conventional vehicles, the driver's command entails the activation of the selected rear light(s) of both the tractor rear light set and the trailer rear light set. This results in a useless fuel consumption for activating the rear lights of the tractor.
It therefore appears that there is room for improvement in the operation of vehicles rear light sets.
It is desirable to provide a method for controlling the operation of a rear light set of a vehicle tractor which can be improved in terms of fuel consumption.
In case no trailer is connected to the tractor, the tractor rear light set can be operated as usual. On the contrary, when a trailer is connected to the tractor, the trailer rear light set replaces the tractor rear light set to provide the necessary information to a person outside the vehicle.
On the one hand, the method according to the invention provides deactivating the rear light(s) of the tractor rear light set when they cannot be seen by a person outside the vehicle because of the trailer, these rear light(s) thus being useless. This typically occurs when the tractor and the trailer are aligned or when the angle between their longitudinal axes is fairly low.
On the second hand, the method according to the invention provides activating the rear light(s) of the tractor rear light set even if a trailer is connected to the tractor and has the same rear light activated, in case the tractor rear light has become apparent/perceptible by a person outside tire vehicle. This typically occurs when the truck is turning, which results in the tractor and trailer axes not being aligned any more: in such a position, some rear light(s) of the tractor, or the beam emitted by said lights, are no longer hidden by the trailer but can be seen laterally. Then, the tractor rear light set and trailer rear light set duplicate each other and improve the vehicle overall system of light signals.
Thus, the invention makes it possible to reduce the vehicle fuel consumption without impairing safety, but activating the rear lights of the tractor rear light set only when necessary.
It has to be understood that the condition a>ath—or a<ath—is expressed in terms of absolute value.
According to an embodiment, the rear light of the tractor rear light set which is of the same type as the activated rear light of the trailer rear light set and which is located inside of the turn, if it exists, is maintained deactivated in the manoeuvring operation.
Indeed, said rear light of the tractor rear light set is generally not perceptible as it is hidden by the trailer when the vehicle is turning. With a method allowing controlling independently the rear lights of the tractor rear light set pertaining to a same pair, the method further improves fuel consumption. Alternatively, for example in order to simplify the controlling system, it could be envisaged to activate both rear lights of the pair, i.e. the rear lights of the tractor rear set which are of the same type and which are located on the outside/on the inside of the turn.
In the manoeuvring operation, the method according to the invention may comprise activating all the rear lights of the tractor rear light set which are of the same type as one activated rear light of the trailer rear light set and which are located at least partially beyond a trailer outside wall. In other words, ath is determined to achieve this result.
In the manoeuvring operation, the method according to the invention may comprise activating all the rear lights of the tractor rear light set which are of the same type as one activated rear light of the trailer rear light set and which emit a beam that can be seen by a driver of another vehicle or by a pedestrian. In other words, ath is determined to achieve this result.
Said predetermined threshold (ath) can range from 0.5° to 8°. For example, ath can be around 5°.
It may be envisaged to set a single threshold ath for all rear lights of the tractor rear light set. Alternatively, it may be envisaged to set a specific threshold ath for each given rear light of the tractor rear light set, depending on the distance between said given rear light and the tractor longitudinal median plane. Indeed, the farer a rear light is located from said plane, the sooner it becomes apparent when the vehicle turns, meaning the lower the threshold ath can be.
The method may further comprise deactivating all the rear lights of the tractor rear light set if a trailer is detected to be connected to the tractor, if there is at least one activated rear light in the trailer rear light set, and if the steering angle of the vehicle is below the predetermined threshold. In other word, in such an embodiment, it is not only the rear light(s) of the tractor rear light set which is (are) of the same type as the activated rear light of the trailer rear light set which is deactivated. This entails a further decrease in fuel consumption.
The steering angle of the vehicle can be detected:                using a sensor of the steering wheel angle;        using a sensor of the steering of the tractor wheels;        and/or using a sensor of the angle between the tractor longitudinal axis and the trailer longitudinal axis.        
In practice, the rear light set can comprise at least one rear light among: a position light, a brake light, a reverse light, a fog light, a direction indicator.
The vehicle may further comprise a steering wheel angle sensor, a tractor wheel steering sensor, and/or an angle sensor capable of detecting the angle between the tractor longitudinal axis and the trailer longitudinal axis.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.